In general, design changes come up in the final phase of the circuit design, which need to be implemented without affecting the processed sections. These changes are conventionally known as an engineering change order (ECO). In order to satisfy the need to implement these ECOs, spare circuitry is normally included in the circuit design. Spare latches are an example of this spare circuitry and are often used to implement the ECOs.
Spare latches, which are initially not part of a data path or logic circuit, are often spread out within a design pattern. When necessary, a circuit or physical design engineer typically selects spare latches that appear to be nearest to a desired location on the chip. However the closest spare latch may not be the best from a timing and routing point of view. Typically, the logic designer does not have the ability to reliably choose a correct spare latch which will close design from a timing point of view. For example the nearest spare latch may be in a different clock gating domain from the data path into which the designer may wish to insert it.